1. Field of the Invention
The invention pertains generally to a pipette for a pipette system. In particular, the invention is directed to a pipette for the handling of a syringe and includes jaw chucks which are adjustably arranged with respect to a plunger receptacle which is pivotally mounted on a plunger-gripping device. The syringe is received in the jaw chucks in manner such that the plunger head is in marginal contact with the jaw chucks, the jaw chucks being laterally engageable on the plunger head A upon the insertion of the syringe. The engaging movement of the jaw chucks on the plunger head is regulated in a manner such that, with respect to a surface of the plunger head, the engaging movement has a substantially tangential component. As a result, a desired and form-locking connection to the plunger head of the syringe results that requires a small amount of force.
2. Description of Related Art
German Patent DE 43 41 229 C1 discloses a pipette system in which a pipette-operated syringe can be axially inserted into the pipette, or, respectively, removed from the pipette. In such a system, the affixing of the cylinder and plunger of the syringe is made using radially adjustable cylinder-gripping and plunger-gripping levers. The cylinder-gripping lever and the plunger-gripping lever are elastically forced into their gripping position and can be brought into a releasing position against the elastic force. The invention also includes an actuating element on the pipette housing is used which is hand-operated against the elastic force.
German Patent DE 29 26 691 C2 discloses a pipette system having syringes that can be axially inserted, but are complicated regarding the design of the cylinder-gripping device and the plunger-gripping device. Pipettes having a more simplistic construction have syringes that can be radially inserted into and removed from the pipette. The present invention is based upon such a pipette.
In a conventional pipette, the cylinder-gripping device has a radially accessible and permanently mounted on the pipette housing, and is designed as a flange-like ring with a U-shaped top view having a cantilever spring found vertically above it. This cantilever spring supports the fastening section of the syringe cylinder, which is designed as a circular, projecting flange, after radial insertion. The plunger head of the syringe plunger, which juts upward from the cylinder, is lead laterally into a plunger receptacle on the plunger-gripping device simultaneously with the insertion of the cylinder flange. The plunger receptacle is formed by two flanking jaw chucks which together form a U-shape and which grip the plunger head from the side and clamp it tight during the insertion of the syringe.
An actuating device is mounted on the plunger-positioning device, and is a part of the plunger-gripping device of the plunger-positioning device. The actuating device is a hinged, clamping component that is opened upwardly for the insertion of the syringe and swung down for the final fixation of the plunger head between the jaw chucks. In the down-swing, the jaw chucks, which are already firmly on the plunger head anyway due to their own elastic force, are additionally pressed against the plunger head.
Moreover, the conventional pipette system has an axially working clamp spring which forms such an insertion bevel. However, its elastic force must be very high in order to achieve an axial movement of the plunger in the pushed-in position despite the clamping force of the already clampingly-engaged jaw chucks.
To guarantee a secure position of an inserted plunger head between the jaw chucks, each jaw chuck is provided with an edging, and particularly with a serrated edge. With the complying choice of material for the plunger head, the edging is pressed into the material of the plunger head from the side, especially when dealing with a serrated edge, so that, in respect to the substantial axial forces which are transferred from the plunger-positioning device to the plunger head during operation, not only a friction joint between jaw chucks and plunger head results, but also, to a certain extent, a positive or form joint.
It has been seen in practice that the above-mentioned prior art construction is capable of improvement in different respects. For one, for the insertion into the pipette, a substantial lateral force must be exerted on the syringe. The syringe cylinder has no problems absorbing this force. Problems arise in plungers and plunger heads, especially with slimmer syringes. The plunger head must be pressed between the jaw chucks and the plunger-gripping device with considerable force. This force can sometimes only be applied by means of pushing on the plunger head itself If one tries to do so only through force transfer by means of the cylinder, it can occur that the plunger head breaks off or is only crooked in the plunger-gripping device making it non-functional.
Furthermore, during the insertion of the plunger head between the laterally placed jaw chucks, a positive pre-fixation of the plunger results in the axial direction also. As soon as the syringe is inserted, one can no longer axially push the plunger head (plunger not yet fully in position), which was possibly positioned somewhat too high during insertion. The syringe must be removed and then re-inserted with a fully inserted plunger.
The actuating device, designed as a hinged cover, for the plunger-gripping device must have a hand-operated element in order for it to be moved. This hand-operated element is disturbing during the operation of a hand-held pipette because it is, necessarily, axially pushed together with the plunger-positioning device in the pipette housing. On the one hand, a corresponding path must therefore be kept free for insertion into the pipette housing. On the other hand, the hand operation collides with the hand holding the pipette. Consequently, problems occur in the case of an ergonomically useful design of the pipette in which the user s hand wraps fully around the pipette housing.
The object of the invention is to overcome the aforementioned difficulties for a pipette in which a syringe is radially inserted. In accordance to the present invention, the pipette includes jaw chucks that are placed to the side of the plunger head of the syringe, and have little, if no, effect during the insertion of the syringe, and are engaged on the plunger head of the syringe only after a successful insertion of the syringe. Using this method, the more sensitive plunger head can be inserted into the plunger receptacle practically without the use of large amounts of force. Thereby, the axial pre-fixation of the plunger head is excluded so that in case of an emergency, the plunger, should it extend too far beyond the end of the cylinder, can be pushed downward even if the syringe is still in place. This can also occur automatically, for example, with an insertion bevel on the closed end of the plunger receptacle of the plunger-gripping device opposite the open end of the pipette housing. Moreover, it is possible to omit the hinged cover as an actuating device for the plunger-gripping device on the movable plunger-positioning device in the case of a corresponding design of a pipette according to the invention. More so, a fixed activating device can be relatively easily implemented for the plunger-gripping device.
In an exemplary embodiment of the present invention, the force necessary for forming an adequate, form-locking connection of the jaw chucks on the plunger head is small since an engaging or positioning movement of the jaw chucks is regulated in a manner such that it has a substantially tangential component with respect to the surface of the plunger head. In addition, the jaw chucks are provided with a serrated edge so that the production of the necessary, form-locking connection for the application of substantial axial traction results not only by convertibly pressing the serrated edge into the plunger head with very high forces, but also by cutting into the material of the plunger head following the tangential movement. It must be taken into consideration that for a normal pipette, depending on the viscosity of the liquid to be pipetted, forces up to 70 N or more must be transferred in the axial direction. Of course, every possibility of slippage between the plunger-positioning device and the plunger head must be avoided in order to adhere to the desired exactness of dosage. Thereby, this form-locking connection, created with the lowest possible forces, is of considerable importance.
Generally, the engaging movement of the jaw chuck can be created by a hand operation of the actuating device. However, it is more practical to create the higher forces applied by the serrated edge for cutting into the plunger head with hand operation of the actuating device, but to achieve the positioning itself by xe2x80x94the elastic force of the engaging springs. This especially makes a permanent arrangement of the actuating device on the pipette housing possible. The actuating device is only used for the application of force in the beginning and for later forcing the jaw chucks apart. Therefore, it must be ready for use only for plungers which are entirely or mostly inserted into the cylinder. Thus, the actuating device can be removed from the movable plunger-positioning device and can be permanently arranged on the pipette housing with all the advantages for the manageability of the pipette according to the invention.
The invention will be better understood and the above objects will become more apparent in the following detailed description of the preferred embodiments of the invention, with reference to the accompanying drawings.